[026 AQUATIC PHYCOMYCETES 



a hyphal branch protruding from a rotifer, rounded cysts and a group 

 of about eight bodies of amoeboid shape which were simultaneously 

 twisting and oscillating. The moving bodies soon came to rest and 

 encysted. When next observed they had apparently emerged from their 

 cysts, each through a short germ tube. Arnaudow (1921) describes the 

 zoosporangium as similar to the completely filamentous type found in 

 certain species of Pythium and asserts that the zoospores are formed as in 

 that genus. His observations on this process have been confirmed by 

 Prowse (1954b). Middleton (1952) states that a discrete vesicle is 

 sometimes not present. Zoospore formation was not seen by Karling 

 (1936c) in Z .tentaclum (see the discussion under Z. insidians). Sexual 

 organs have been described, but apparently only by Arnaudow 



(1925). 



Valkanov (1932) considered that the carnivorous aquatic fungi Syn- 

 chaetophagus (Apstein, 1910), Hydatinophagus, and Sommerstorffia 

 (Arnaudow, 1923a, 1923b) were closely related to Zoophagus and that 

 all four should be placed in a special group of the Saprolegniaceae. The 

 reasons he gave were not convincing. From the morphological evidence 

 now at hand, it seems much more likely that this curious carnivorous 

 habit has been separately evolved by members of several distinct groups 

 of aquatic Phycomycetes. 



KEY TO THE SPECIES OF ZOOPHAGUS 



( apturing organ consisting of an unbranched peglike lateral branch 



Z. insidians, p. 1026 

 Capturing organ consisting of a short lateral branch, from which arise 



apically from one to five long slender tentacles . . . Z. tentaclum, p. 1029 



Zoophagus insidians Sommerstorff 



Osterr. botan. Zeitschr., 61 : 372, pis. 5-6. 1911 

 (Fig. 85 A-G, p. 1029) 



Mycelium slender, the main hyphae 6-7 \x in diameter, sparingly 

 branched, frequently ramifying between and upon algae, forming nu- 

 merous lateral unbranched spinelike or peglike apically refractive cap- 



